Carrie Yin Kwan Chan

Molecular anchors in the solid state: Restriction of intramolecular rotation boosts emission efficiency of luminogen aggregates to unity

Introduction of freely rotatable tetraphenylethene (TPE) to conventional luminophors quenches their light emissions in the solutions but endows the resultant molecules (TPEArs) with aggregation-induced emission characteristics in the condensed phase due to the restriction of intramolecular rotation. High fluorescence quantum yields up to 100% have been achieved in the films of TPEArs.

Stereoselective Synthesis, Efficient Light Emission, and High Bipolar Charge Mobility of Chiasmatic Luminogens

Stereoregular tetraphenylethene derivatives (Z)-o-BCaPTPE and (Z)-o-BTPATPE featured with chiasmatic conformations and aggregation-enhanced emission characteristics are synthesized using a McMurry reaction. Both luminogens exhibit high hole and electron mobilities. Organic light-emitting diodes (OLEDs) using (Z)-o-BCaPTPE and (Z)-o-BTPATPE as both the light-emitting and electron-transporting layers show high efficiencies.

Using tetraphenylethene and carbazole to create efficient luminophores with aggregation-induced emission, high thermal stability, and good hole-transporting property

Tetraphenylethene (TPE) is an archetypal luminogen that exhibits a phenomenon of aggregation-induced emission (AIE), while carbazole is a conventional chromophore which shows the opposite effect of aggregation-caused quenching (ACQ) of light emission in the condensed phase. Melding the two units at the molecular level generates a group of new luminescent materials that suffer no ACQ effect but depict high solid-state fluorescence quantum yields up to unity, demonstrative of the uniqueness of the approach to solve the ACQ problem of traditional luminophores. All the TPE–carbazole adducts are thermally and morphologically stable, showing high glass-transition temperatures (up to 179 °C) and thermal-degradation temperatures (up to 554 °C). Multilayer electroluminescence devices with configurations of ITO/NPB/emitter/TPBi/Alq3/LiF/Al are constructed, which exhibit sky blue light in high luminance (up to 13 650 cd m−2) and high current and external quantum efficiencies (up to 3.8 cd A−1, and 1.8%, respectively). The devices of the luminogens fabricated in the absence of NPB or hole-transporting layer show even higher efficiencies up to 6.3 cd A−1 and 2.3%, thanks to the good hole-transporting property of the carbazole unit.

Synthesis, Structure, Aggregation-Induced Emission, Self-Assembly, and Electron Mobility of 2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)(2) (C-C≡C-SiPh(3))(2)] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10(-5) cm(2) V(-1) s(-1) was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.

Aggregation-induced emission, mechanochromism and blue electroluminescence of carbazole and triphenylamine-substituted ethenes

Carbazole and triphenylamine-substituted ethenes are synthesized [Ph2CCPh(R), R = 9-carbazolyl, 9-hexyl-3-carbazolyl and 4-(diphenylamino)phenyl] and their optical properties are investigated. All luminogens are nonemissive when molecularly dissolved in good solvents but become highly emissive in the aggregated state, showing a phenomenon of aggregation-induced emission. High solid-state fluorescence quantum yields up to 97.6% have been achieved in their solid thin films. The luminogens are thermally stable, showing high degradation temperatures of up to 315 °C. They exhibit mechanochromism: their emissions can be repeatedly switched between blue and green colors by simple grinding–fuming and grinding–heating processes due to the morphological change from crystalline to amorphous state and vice versa. Multilayer light-emitting diodes with device configurations of ITO/NPB/dye/TPBi/Alq3/LiF/Al, ITO/NPB/dye/TPBi/LiF/Al and ITO/dye/TPBi/LiF/Al are fabricated, which emit sky blue light with maximum luminance, current efficiency, power efficiency and external quantum efficiency of 11 700 cd m−2, 7.5 cd A−1, 7.9 lm W−1 and 3.3%, respectively.

Highly fluorescent and photostable probe for long-term bacterial viability assay based on aggregation-induced emission.

Long-term tracking of bacterial viability is of great importance for monitoring the viability change of bacteria under storage, evaluating disinfection efficiency, as well as for studying the pharmacokinetic and pharmacodynamic properties of antibacterials. Most of the conventional viability dyes, however, suffer from high toxicity and/or poor photostability, making them unsuitable for long-term studies. In this work, an aggregation-induced emission molecule, TPE-2BA, which can differentiate dead and living bacteria and serve as a highly fluorescent and photostable probe for long-term viability assay. TPE-2BA is a cell-impermeable DNA stain that binds to the groove of double-stranded DNA. Bacteria with compromised membrane open the access for TPE-2BA to reach DNA, endowing it with strong emission. The feasibility of using TPE-2BA for screening effective bactericides is also demonstrated. Plate count experiment reveals that TPE-2BA poses negligible toxicity to bacteria, indicating that it is an excellent probe for long-term bacterial viability assay.

Construction of efficient solid emitters with conventional and AIE luminogens for blue organic light-emitting diodes

9,9-Bis(9-heptyl-3-carbazolyl)fluorenes (BPyBCF, BAnBCF, BTPABCF, and BTPEBCF, where B = Bis, Py = pyrene, C = carbazole, F = fluorene, An = anthracene, TPA = triphenylamine, and TPE = tetraphenylethene) with different chromophoric units at the 2,7-positions are synthesized in moderate to high yields (52–89%) by Suzuki coupling reactions of 9,9-bis(9-heptyl-3-carbazolyl)-2,7-dibromofluorene with the corresponding arylboronic acid and utilized as active layers for the construction of blue organic light-emitting diodes (OLEDs). BPyBCF, BAnBCF and BTPABCF emit intense blue light with high fluorescence quantum yields (ΦF = 75–94%) in solution. However, they exhibit much lower ΦF values (30–61%) in the film state, revealing that aggregate formation has quenched their light emission. On the contrary, BTPEBCF is weakly emissive in solution (ΦF = 0.3%) but becomes a strong emitter (ΦF = 100%) when fabricated into solid film, demonstrating a phenomenon of aggregation-induced emission (AIE). Restriction of intramolecular rotation and suppression of intermolecular interactions due to the propeller-like tetraphenylethene unit are responsible for the AIE phenomenon. All the luminogens are thermally and morphologically stable, showing high glass-transition (Tg = 109–147 °C) and thermal-degradation temperatures (Td = 396–478 °C). Non-doped OLEDs using BPyBCF, BAnBCF, and BTPABCF as light-emitting layers are constructed, which give blue electroluminescence with maximum current (ηC,max) and external quantum (ηext,max) efficiencies of 4.8 cd A−1 and 2.3%. With the same device configuration, BTPEBCF shows higher ηC,max and ηext,max values of 7.9 cd A−1 and 2.9%, respectively, thanks to its AIE feature.

An aggregation-induced-emission platform for direct visualization of interfacial dynamic self-assembly.

An in-depth understanding of dynamic interfacial self-assembly processes is essential for a wide range of topics in theoretical physics, materials design, and biomedical research. However, direct monitoring of such processes is hampered by the poor imaging contrast of a thin interfacial layer. We report in situ imaging technology capable of selectively highlighting self-assembly at the phase boundary in real time by employing the unique photophysical properties of aggregation-induced emission. Its application to the study of breath-figure formation, an immensely useful yet poorly understood phenomenon, provided a mechanistic model supported by direct visualization of all main steps and fully corroborated by simulation and theoretical analysis. This platform is expected to advance the understanding of the dynamic phase-transition phenomena, offer insights into interfacial biological processes, and guide development of novel self-assembly technologies.

Stoichiometric imbalance-promoted synthesis of polymers containing highly substituted naphthalenes: rhodium-catalyzed oxidative polycoupling of arylboronic acids and internal diynes

A new route for the synthesis of functional polymers was developed. Oxidative polycoupling of 4,4′-(α,ω-alkylenedioxy) bis(diphenylacetylene)s with phenylboronic acid and (1,1,2-triphenylvinyl)phenylboronic acid, respectively, was catalyzed by [Cp*RhCl2]2 and oxidants in dimethylformamide, affording soluble polymers with highly substituted naphthalene rings in satisfactory yields with moderate molecular weights. All the polymers were thermally and morphologically stable, showing high thermal-degradation and glass-transition temperatures of 317–404 °C and 95–168 °C, respectively. They were film-forming and their thin solid films showed high refractive indices (RI = 1.7414–1.6038) in a wide wavelength region of 400–1600 nm. The polymer carrying tetraphenylethene unit was weakly emissive in solution but emitted intensely in the condensed phase, displaying a phenomenon of aggregation-induced emission. The emission of its nanoaggregates could be quenched by picric acid with large quenching constants, making it promising as a sensitive chemosensor for efficient detection of explosives.

Luminescent tetraphenylethene-substituted silanes

Tetraphenylethene (TPE)-substitued silanes [(Ph4C=C)mSi(Ph)n, m = 3–1, n = 3–1] are designed and synthesized, and their optical, thermal, and electrochemical properties are studied. Whereas they are nonluminescent in solutions, they become highly emissive when aggregated in poor solvents (such as water) or fabricated into thin films, demonstrating a novel phenomenon of aggregation-induced emission (AIE). Their amorphous films exhibit high fluorescence quantum yields (54.6–63.7 %). They enjoy high thermal stability with 5 % weight loss occurring at 320–420 °C. Multilayer electroluminescence (EL) devices (ITO/NPB/emitter/TPBi/LiF/Al) utilizing the silanes as emitting layers are fabricated, which give deep blue EL with maximum luminance and external quantum efficiency of 5672 cd/m2, and 1.6 %, respectively.